Conventionally, there has been known a battery system which includes a plurality of flat secondary batteries (see JP 2014-44884 A). To be more specific, the battery system includes: the plurality of flat secondary batteries respectively having electrode terminals and are stacked in a thickness direction; bus bars each connecting the electrode terminals of the flat secondary batteries disposed adjacently to each other; and intermediate reinforcing plates each disposed between the flat secondary batteries.
The bus bar is a conductive member having a flat plate shape which extends straightly in a stacking direction of the flat secondary batteries. Both ends of the bus bar are respectively fixed to the above-mentioned electrode terminals to be connected. The electrode terminals of the flat secondary batteries disposed on both sides of the intermediate reinforcing plate are also connected to each other by the bus bar. The battery system further includes bind bars and end plates which apply a pressure to the flat secondary batteries in the stacking direction. The intermediate reinforcing plate is fixed to the bind bars by screws.
In the battery system, when acceleration in the stacking direction of the flat secondary batteries is generated, since the intermediate reinforcing plate is fixed to the bind bars, there may be a case where a difference is generated between a moving amount of the flat secondary battery on one side of the intermediate reinforcing plate and a moving amount of the flat secondary battery on the other side of the intermediate reinforcing plate in the stacking direction so that a distance between the flat secondary battery changes.
In this case, in the bus bar which connects the electrode terminal of the flat secondary battery on one side and the electrode terminal of the flat secondary battery on the other side to each other, a stress caused by a change in the above-mentioned distance is concentrated on a connecting portion between the electrode terminals and hence, the connecting portion is liable to be damaged.
Such a phenomenon may also occur in a case where a total terminal of the battery system which is used for inputting and outputting of electricity to and from the outside is fixed to the end plate. That is, when a difference is generated in moving amount between the total terminal fixed to the end plate and the electrode terminal of the flat secondary battery so that the distance changes, in the bus bar which connects the total terminal and the electrode terminal to each other, a stress caused by such a change is concentrated on the electrode terminal or connecting portions with the total terminal and hence, such portions are easily damaged.